The selective call network systems of today have proven to be very effective in reaching people who cannot be tied to a telephone. Selective call network systems are conventionally divided into two types. Some network systems, called wide area network systems, allow for transmission of messages to a large number of users in a large area, such as a metropolitan area. The wide area network systems meet the needs of sales and service people who are constantly on the move within an urban area. With a large number of users, though, the selective call messages must necessarily have a short transmission time, such as comprising an alert plus a short numeric message.
Other network systems designed for persons who are frequently away from their desks, but seldom leave their campus (e.g., the factory, office building, or hospital in which they work) have a localized coverage area, some even solely within one building. These network systems are called local area or on-site selective call network systems and conventionally provide longer voice messages to a smaller number of users who need more information than can be provided in a short numeric message.
Each selective call network system, whether wide area or on-site, is assigned a unique frequency in a manner such that systems proximately located to each other will operate on distinct and separate selective call communications paths or frequencies called channels.
With the proliferation of selective call services, a class of users of selective call receivers has arisen who receive messages on more than one selective call network system. For example, the user subscribes to a wide area network system receiving selective call messages when off campus and subscribes to at least one on-site network system for receiving selective call messages when on campus. Doctors, for instance, may need to be on call when they are off duty and away from the hospital and thus, require the services of a wide area network system. However, when the doctors are on duty at the hospitals, they need the services of an on-site network system.
It is desirable that the reception of a message by a selective call receiver (e.g., a pager) have a high probability of reception. To increase the probability of message reception, a user subscribing to two selective call network systems may use two selective call receivers: one for the wide area network and one for the on-site network. Yet this is expensive and inconvenient. But a single selective call receiver, even if able to receive signals on multiple channels, can only monitor one channel at a time. If the selective call receiver is tuned to an on-site selective call system channel, it cannot simultaneously receive transmissions from the surrounding wide area network system on a different channel. Manual selection of the operating channel is undesirable because of the possibility of missed messages due to nonselection or misselection of channels.
In addition, it is desirable that a user subscribing to two network systems be able to receive selective call messages broadcast from both network systems. If a selective call message is being transmitted for the user by a wide area network system and the user is in a building, there can be difficulty in reception because of the interference of the surrounding building. The selective call receiver may scan between the wide area and on-site channels to increase the probability of message reception. An example of two channel scanning is described in U.S. Pat. No. 4,644,347 assigned to the assignee of the present invention. While a selective call message is being received on one channel, though, the other channel is not scanned. A message transmitted for a user on one channel, therefore, could not be received by the user if he is receiving a message concurrently on another channel.
Thus, what is needed is a network system and a selective call receiver for increased reliability of selective call message reception in both an on-site selective call network system and the surrounding wide area selective call network system operating essentially automatically and permitting the user to receive selective call messages broadcast from one network system while tuned to the channel of the other network system.